dual camera for stereo

the description about tegra K1’s CSI list 3 ways for users to interface the port.
one of them is 2 x4(dual camera for stereo with 4 lanes for each camera), so i guess there must be no less than 20 pins of CSI interface.but the pin list of CSI is; CSI_A_CLK_N/P、CSI_A_D0_N/P、CSI_A_D1_N/P、CSI_B_D0_N/P、CSI_B_D1_N/P、CSI_E_CLK_N/P、CSI_E_D0_N/P, this really puzzled me, could someone explain it?

Which document you refer to?
The TegraK1_Embedded_DG have clear CSI Configuration table show how to map CSI.

CSI.jpg

The ball DSI_B_CLK/D[0:3] can be used as the second x4 CSI interface.